There are growing demands for 3D structure determination of nucleic acids and protein-nucleic acid complexes for understanding disease molecule-level mechanisms and discovering new drugs. X-ray crystallography is one of the most direct and powerful tools for structure determination of these macromolecules and complexes. However, the crystallization and heavy atom derivatization for phase determination have largely slowed down structural determination of new structures and folds. Therefore, developing novel technologies that allow the phase determination and crystallization facilitation is of tremendous value. Recently the PI and his research group have pioneered and successfully demonstrated a novel derivatization strategy via replacement of oxygen of nucleic acids with selenium. Their research is based on their central hypothesis that since oxygen and selenium are in the same elemental family, selenium can be used to stably replace oxygen of nucleic acids atom- specifically without significant perturbation. They have successfully demonstrated that their selenium derivatization of nucleic acids can be used to solve the phase problem. Furthermore, they have discovered that the Se-derivatization can largely facilitate crystallization of DNAs. Therefore, their Se-derivatization strategy has great potential to provide novel and rational solutions to these two long- standing problems, leading to new and valuable products and services. Though they have already synthesized many Se-derivatized phosphoramidites and triphosphates (the building blocks), their relatively-low synthetic scales and inefficient purification protocols limit them to synthesis of a small number and quantity of Se-DNAs and Se-RNAs for crystallization, structure and function characterizations. These synthesis and purification problems largely limit the applications of their novel technologies. In this Phase I research project, they plan to increase the phosphoramidite synthesis to the gram scale (10 fold increase from their current scale), and the Se-triphosphate synthesis to the 100-miligram scale (50-100 fold increase from their current scale). Their primary objectives in this Phase I project are to develop efficient synthesis procedures and purification protocols for the Se-building blocks and DNAs &RNAs modified with selenium. In addition, they will also explore crystallization of nucleic acids with selenium derivatization. Ample preliminary results strongly support the feasibility of the proposed work, and the research team has extensive expertise in the proposed research areas. Their long-term goal is to fully establish the standard and convenient strategies for the rational phasing and crystallization of nucleic acids via the selenium derivatization, in order to service the customers and meet the needs on these novel materials and the 3D structure determination of nucleic acids and their protein complexes. PUBLIC HEALTH RELEVANCE: Selenium-derivatized nucleic acids have great potentials in rational phase determination and crystallization facilitation for 3D crystal structure determination of nucleic acids and their protein complexes, which provide molecule-level disease mechanisms and lead to new drug discoveries and disease treatments.